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bsdmainutils Local Root Compromise
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SUMMARY
<http://packages.debian.org/unstable/utils/bsdmainutils> bsdmainutils is
"a collection of small programs many people expect to find when they use a
BSD-style UNIX system. Included are: banner, ncal, cal, calendar, col,
colcrt, colrm, column, from, hexdump, look, lorder, ul and write".
A vulnerability in its calendar program allows local users to gain root
privileges by causing the program to include sensitive files in its event
notification emails.
DETAILS
Vulnerable Systems:
* bsdmainutils version 6.0.14 and prior
Immune Systems:
* bsdmainutils version 6.0.1 or newer
How calendar works
The calendar program uses event files with this format:
<date><tab><event description>
This is not all however. Calendar gives users the ability to include other
event-files and define variables and macros. To do this, it calls cpp (the
C preprocessor) on the main event file and processes the output.
When called with the "-a" option, calendar will processes the event files
of all users and send the result by mail.
The bsdmainutils package in Debian uses this feature from:
/etc/cron.daily/bsdmainutils. Luckily, it is not enabled by default since
you have to comment an "exit 0" line in the cron script to activate it.
The problem:
Calendar does not drop its privileges. In order to be useful when running
with the "-a" option, it needs to run as root. By creating an event file
as follows, we can get the hashed root password (on June 28th):
#define root Jun. 28<tab>cut_here
#include </etc/shadow>
Jun. 28<tab>Birthday of Steven Van Acker
Aug. 19<tab>Birthday of Andrew Griffith
(<tab> indicates an actual tab, so char '\t')
Since calendar is running as root, there will be no problem accessing the
shadow password file. The result contains the hashed password of root,
which can then be cracked.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0793>
CAN-2004-0793
ADDITIONAL INFORMATION
The information has been provided by <mailto:deepstar@ulyssis.org> Steven
Van Acker.
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